This invention relates to a process for purifying urea-containing waste water by treating the waste water at an elevated temperature and pressure to hydrolyze the urea, and desorbing the ammonia and carbon dioxide thus formed.
In the preparation and processing of urea, a difficulty arises that the urea-containing waste water often obtained cannot be discharged as is to surface waters. Therefore various means have been attempted to remove the urea from this waste water.
Biological waste water purification constitutes a potential solution to this problem, but has a disadvantage that at least a two step purification is always necessary, that is, aerobic and anaerobic purification, and there is no possibility of recovering or recycling the urea or the ammonia that might otherwise be obtained.
Economically, it is preferred to remove and recover the urea and/or ammonia from the waste water. Various methods have been proposed to accomplish this, all of which basically involve the steps of desorbing ammonia and carbon dioxide from the urea-containing waste water, subsequently hydrolyzing the urea contained in the waste water followed by the total or partial desorption of the ammonia and carbon dioxde thus formed. A process of this nature is described in Proceedings, The Fertilizer Institute, Environmental Symposium, 13-16 January, 1976, p. 91 et seq.
However, such a process has the disadvantage that a separate installation consisting of a number of distillation and hydrolysis columns is required to process the urea-containing waste water.
An objective of the present invention is therefore to provide an improved method for the removal of urea from urea-containing waste water in an effective and economic manner. It is a further objective to provide for the removal of urea from urea-containing waste water without the necessity of installing special equipment solely for that purpose. It is a further objective to provide a method for the removal of urea from waste water by hydrolysis and recovering substantially pure ammonia and/or substantially pure carbon dioxide produced thereby.